Photodegradable styrene polymer foams containing a hydrocarbon photosensitizer

ABSTRACT

Expandable styrene polymer particles which are photodegradable are produced by suspending styrene polymer particles in an aqueous medium and impregnating a blowing agent into the particles in the presence of 0.5 - 5.0 parts of photosensitizer per 100 parts of polymer particles. The photosensitizer is selected from the polynuclear hydrocarbons having at least one benzylic methylene group in one of the rings, such as fluorene, acenaphthene, and 9,10-dihydroanthracene.

United States Patent [191 Wright [451 *Nov. 4, 1975 PHOTODEGRADABLE STYRENE 3,798,187 3/1974 Miyoshietal. 260/2.5 POLYMER FOAMS CONTAINING A 3,832,312 8/1974 Wright 260/2.5 HB

HYDROCARBON PHOTOSENSITIZER Harold A. Wright, Murrysville, Pa.

Assignee: Arco Polymers, Inc., Philadelphia,

The portion of the term of this patent subsequent to Augv 27, 1991, has been disclaimed.

Filed: Apr. 5, 1973 Appl. No.:'348,179

Inventor:

Notice:

References Cited UNTTED STATES PATENTS 5/1961 DAlelio 260/2.5 3/1974 Taylor et al. 220/1 OTHER PUBLICATION Polymer Preprints Vol. 13, No. 2 Aug. 1972 pg. 627.

Primary Exami'rter-Eugene C. Rzucidlo Attorney, Agent, or Firm-Lewis J. Young [57] ABSTRACT Expandable styrene polymer particles which are photodegradable are produced by suspending styrene polymer particles in an aqueous medium and impregnating a blowing agent into the particles in the presence of 0.5 5.0 parts of photosensitizer per 100 parts of polymer particles. The photosensitizer is selected from the polynuclear hydrocarbons having at least one benzylic methylene group in one of the rings, such as fluorene, acenaphthene, and 9,10-dihydroanthracene.

'6 Claims, No Drawings This inventionrelates to a process for making foamed styrene polymers photodegradable by incorporating merization can result in upsetting the delicate balance photosensitizers into the-polymer during the impregnais well known. Such particles generally contain a blowing agent which boils below the softening point of thepolymer and which will cause the particles to expand when they are heated. When the expanded particles are heated in a mold cavity, the particles expand further to fill the mold and fuse together to. form a shapedarticle. Examples of articles made by this process are drinking cups, meat packaging trays, egg cartons, fruit packaging trays and the like.

The articles so produced are generally quite stable to sunlight and weather conditions. It is desirable, however, to provide a method whereby discarded foamed articles will degrade under outdoor weather conditions to help disposal problems and prevent litter accumulation Many additives have been developed which accelerate the degradation of plastic articles and much experimentation is being done to develop new systems. The additives are generally added to the polymers by physical mixing, such as blending,.or by simultaneous extrusion of the polymer and additive. One-such additive is benzophenone, a compound known to be a photosensitizer.

SUMMARY or THE INVENTION In accordance with the present invention, photosensitizers selected from the polynuclear hydrocarbons having at least one benzylic methylene group in one of the rings are incorporated into styrene polymer particles during .the process of impregnating the particles with ablowing agent. Incorporation of from 0.5 to 5.0 parts of photosensitizer per 100 parts-ofpolymer gives a foamable product which, when foamed, is degradable by sunlight and weather much morerapidly than is the untreatedpolymer;

DETAILED DESCRIPTION or THE INVENTION In accordance with this invention, a variety of expandable thermoplastic homopolymers andcopolymers can be rendered degradable. The polymers may be derived from vinylaromatic monomers including of convenience, these polymers and copolymers are referred to herein as styrene polymers.

The styrene polymers can, of course, be produced by any of the known techniques. The preferred method of preparation is the suspension technique, which gives head or pellet shaped product.

needed for. the polymerization reaction and would result in interference with the reaction-The addition, in this instance, is to the aqueous suspensi'onin which the particles were prepared and prior to separation of the particles from the aqueous reaction medium. The blowing agent can be added either prior to hard bead formation or simultaneously with the photosensitizer.

Alternatively, particles of styrene polymer may be resuspended in an aqueous medium and impregnated with blowing agent and photosensitizer. In this case, suspending agents are added to thewater to keep the particles from agglomerating at the elevated temperatures used during the impregnation process. Suitable suspending agent systems are, for example, those described in DAlelio US. Pat. No. 2,983,692, such as tricalcium phosphate in combination with an anionic surfactant.

The impregnation is conventionally'carried out at temperatures ranging from about to 150 C. Increasing the temperature makes the impregnation proceed at a faster rate. e

The blowing agents are compounds which are gases or which will produce gases on heating. Preferred blowing agents include aliphatic hydrocarbons containing from l-7 carbon atoms in the molecule, such as methane, ethane, propane, butane, pentane, hexane, heptane, cyclohexane, and their halogenated derivatives which boil at a temperature below the softening point of the polymer. Mixtures of these agents may also be used, such as a mixture of 40-60% n-pentane and 60-40% trichlorofluoromethane. Usually from 3 to 20% of blowing agent per parts of polymer is incorporated by the impregnation.

The photosensitizers useful in the present invention are those polynuclear hydrocarbons having at least one benzlic methylene group in one of the rings. Examples of such photosensitizers are acenaphthene, fluorene,

2,3-benzofluorene, 9,l0-'clihydroanthracene, l,2-ben zofluorene, and the like. The photosensitizers also may be the monoor poly-substituted derivatives of the above hydrocarbons which are substituted in one or more of the nuclear rings. Suitable substituents are, for example, lower alkyl groups having from 1 to 4 carbon atoms in the group, halogen (such as fluorine, chlorine,

and bromine), and hydroxy groups. The substituted de-, rivatives of the hydrocarbons are especially useful:

when higher melting derivatives are desired in order to reduce plasticization effects at the higher concentrations of photosensitizer during the molding of the polymer particles.

The photosensitizer is added to the suspension of polymer particles at the same time as the blowing agent. Best results are obtained when amounts of photosensitizer between0.5 and 5.0 parts per 100 parts of polymer are added. Less than 0.5 part of photosensitiZer does not give sufficiently accelerated rates of degradation, while greater than 5.0 parts of photosensitizer may tend to plasticize the polymer particles and cause difficulty in the molding process.

The invention is further illustrated by the following examples wherein parts are parts by weight unless otherwise indicated.

EXAMPLE 1 To a reactor, there was charged in sequence 100 parts of water, 0.025 part of sodium dodecylbenzenesulfonate, 1.0 part of fluorene, 2.0 parts of tricalcium phosphate, 100 parts of polystyrene beads having a particle size of predominantly through 16 and on 35 mesh,

U.S. Standard Sieve, and 9.0 parts of n-pentane. The mixture was stirred and heated during 1 hour to 90 C. to form a suspension. The suspension was maintained at 90 C. for 3 hours and then the temperature was raised during 0.5 hour to 115 C. and maintained at that temperature for an additional 6 hours. The suspension was cooled to room temperature and acidified to a pH of 1.4 with l-lCl. The beads were separated from the aqueous phase by centrifuge, washed with water, and air dried at room temperature. A control experiment was run using the above procedure omitting the fluorene.

' The beads from the above impregnation process were pre-expanded to a density of about 1.26 pounds per cubic foot (p.c.f.). The pre-expanded beads were then molded into strips of foam 1 X 5 X 1/2 inches of approximately 1.5 p.c.f. density.

"These strips were masked with aluminum foil,

wrapped around the long axis, such that about half the strip was protected. The strips were then placed flat beneath a -watt fluorescent sunlamp such that the exposed half of the strips were about 3 inches from the light. After one 96-hour lamp exposure, the strip containing the fluorene showed gross yellowing and embrittlement compared to the control strip.

The strips were subjected to alternate 96-hour lamp exposure followed by an air jet treatment to remove the embrittled polymer. After 6 such alternate treatments the strip containing fluorene had lost 24.3% of its total weight comparedto only a 9.5% weight loss for the control strip. The fluorene-containing strip had lost 18.9% of its initial thickness.

Similar preparation and treatment of samples containing 0.5, 2.0 and 2.5 parts of fluorene per 100 parts of polystyrene showed that the degradation due to ultraviolet light was greater with greater amounts of the sensitizer. The beads'containing 2.5 parts of fluorene were easily prepared by the process of the invention, but were somewhat difficult to mold into acceptable foam strips due to excessive plasticizing action of the sensitizer on the polystyrene.

When 2,3-benzofluorene (m.p. 209 C.), or 1,2-benzofluorene (m.p. 187 C.) was used in place of the fluorene (m.p. l 12C.) in this same process, samples containing as much as 5.0 parts of photosensitizer per 100 parts of polystyrene were prepared. The beads were not difficult to mold, even at this concentration, because of the higher melting points of the benzo-derivatives.

EXAMPLE I] The procedure of Example 1 was repeated using 1.0 part of 9,10-dihydroanthracene as sensitizer. Foamed strips were exposed under the 20-watt fluorescent sunlamp as in Example I with the result that, after one 96- hour exposure, the strip containing dihydroanthracene showed gross yellowing and embrittlement compared to the control strip.

4 Plaques, 5 X 5 X l/2 inches and about 1.5 p.c.f. density, were molded from the expandable beads and exposed to weather in Arizona for 3 months. To supplement the normal weather conditions, the samples were subjected to artificial rain spray equivalent to about 1 inch accumulation once every other week. For comparison, plaques were also molded from beads containing no sensitizer (control) and from beads containing 2.0

parts of fluorene. The control sample turned dark yellow, became moderately brittle,and was eroded to a depth of less than 0.5 mm. The samples containing the 2% of fluorene and the 1% of dihydroanthracene turned very dark yellow, became grossly brittle, and were eroded to a depth of about 1.0 mm.

EXAMPLE III The impregnation process of Example 1 was repeated except that the fluorene was replaced by 1.0 part of acenaphthene and the polystyrene beads were replaced by smaller beads having a particle size of predominantly through 20 and on 40 mesh, U.S. Standard Sieve.

The beads from the above impregnation process were pre-expanded to a density of about 34 p.c.f. and then molded into 6 X 6 inches X mils plaques using a steam press.

The plaques were masked with aluminum foil and exposed to a sunlamp as in Example 1. After one 96-hour exposure the samples containing acenaphthene showed gross yellowing and embrittlement compared to the control plaques.

Identical plaques were exposed to outdoor weather (sum-wind, and rain) in racks at Monroeville, Pennsylvania for 4 weeks. The control samples were off-white and showed little effects of erosionof the surface after the 4-week treatment. Those containing acenaphthene had turned dark yellow and showed signs of erosion and pitting of the surface in the same test.

What is claimed is: v

' 1. A process for making expandable styrene polymer particles containing a photosensitizer comprising suspending styrene polymer particles with the aid of a sus-. pending system in water containing from 3 to 20 per cent by weight of a blowing agent and a photosensitizer, heating the suspension at a temperature of from 80 to 150C. to impregnate the polymer particles, and separating the impregnated particles from the water; said photosensitiz er being present in an amount of 0.5-5.0 parts per 100 parts of said polymer particles and being selected from the polynuclear hydrocarbons having at least one benzylic methylene group in one of the rings.

2. The process of claim 1 wherein said polynuclear hydrocarbon is fluorene.

3. The process of claim 1 wherein said polynuclear hydrocarbon is 9,10-dihydroanthracene.

4. The process of claim 1 wherein said polynuclear hydrocarbon is acenaphthene.

5. The process of claim 1 wherein said polynuclear hydrocarbon is 2,3-benzofluorene.

6. The process of claim 1 wherein said polynuclear hydrocarbon is 1,2-benzofluorene. 

1. A PROCESS FOR MAKING EXPANDABLE STYRENE POLYMER PARTICLES CONTAINING A PHOTOSENSITIZER COMPRISING SUSPENDING STYRENE POLYMER PARTICLES WITH THE AID OF A SUSPENDING SYSTEM IN WATER CONTAINING FROM 3 TO 20 PER CENT BY WEIGHT OF A BLOWING AGENT AND A PHOTOSENSITIZER, HEATING THE SUSPENSION AT A TEMPERATURE OF FROM 80* TO 150*C. TO IMPREGNATE THE POLYMER PARTICLES, AND SEPARATING THE IMPREGNATED PARTICLES FORM THE WATER, SAID PHOTOSENSITIZER BEIGN PRESENT IN AN AMOUNT OF 0.5-5.0 PARTS OF SAID POLYMER PARTICLES AND BEIGN SELECTED FROM THE POLYNUCLEAR HYDROCARBONS HAVING AT LEAST ONE BENZYLIC METHYLENE GROUP IN ONE OF THE RINGS.
 2. The process of claim 1 wherein said polynuclear hydrocarbon is fluorene.
 3. The process of claim 1 wherein said polynuclear hydrocarbon is 9,10-dihydroanthracene.
 4. The process of claim 1 wherein said polynuclear hydrocarbon is acenaphthene.
 5. The process of claim 1 wherein said polynuclear hydrocarbon is 2,3-benzofluorene.
 6. The process of claim 1 wherein said polynuclear hydrocarbon is 1,2-benzofluorene. 